Control system



Feb. 29, 1944. G. a sToLTz CONTROL SYSTEM Filed Feb. 21, 1942 INVENTORGZen/zEStoZZz.

Patented Feb. 29, 1944 CONTROL SYSTEM- Glenn E. Stoltz, Pittsburgh, Pa.,

assignor to Westinghouse Electric Manufacturing Company,

a corporation of Pennsyl- East Pittsburgh, PL,

vania Application February 21, 1942, Serial No. 431,886

14 Claims.

My invention relates, generally, to control systems and, moreparticularly, to systems Ior controlling steel strip rolling mills.

In the operation of steel strip rolling mills, it is necessary that themill speed be reduced very considerably when the end of a new coil ofstrip is threacied through the mill ln order to enable the strip to beproperly threaded into the mill rolls. In the operation of tandem striprolling mills, it has been the practice to slowthe mill down to such aspeed that the rolls of the last roll stand are rotating at the desiredthreading speed. Since the speeds o: all of the roll stands are variedsimultaneously and since the speeds of th stands ahead of the last rollstand decrease progressively toward the nrst roll stand. when the speedof the mill is so decreased as to produce the desiredthreading speed onthe last roll stand, the speeds of the preceding roll stands are verylow and the time, required for threading the end of strip through theseveral roll stands is very long.

It is an object of my invention to provide a control system for a tandemstrip rolling "mill which shall function to so control the mill as topermit threading of the mill in a minimum length of time.

Another object of the invention is to provide a control system for atandem strip rolling mill which shall function automatically to providethe desired threading speed for each succeeding roll stand as the end ofa strip which is being threaded through the mill approaches each of, thestands.

' These and other objects and advantages will be apparent from thefollowing detailed description taken in connection with the accompanyingdrawing, the single figure of which isa diagrammatic representation of atandem strip rolling mill contro1 system embodying the principalfeatures of the invention.

In practicing the invention, a main generator 2 is connected to energizea main bus comprising conductors 4 and 6 from which the armatures of themotors 0, I0, I2, and 14 receive their energization. The motors 8, l0,I2, and H drive reducing roll stands ls, I8, 20, and 22 of a continuousstrip rolling mill. The excitation of the main generator 2 may be variedby a Variable resistor 24 driven by a motor 20 tc thereby vary thespeeds of the motors 8, I0, I2, and I4 simultaneously. lZhe motor 26 iscontrolled by a. reversing circuit contro1 device 28, which, in turn, iscontrolled by load responsive relays 30, 32, and 34, and speedresponsive pilot generators 36, 30, 40, and 42 under the control of a.circuit control device 44.

Considering the invention more in detail, the reversing circuit controldevice 20 may be controlled by the selective operation of a pair ofpotential responsive relays 46 and 48 through their contact elements'and 52, respectively. When the relay 46 is actuated and its contactelement b0 is in th upper circuit closing position, an energizingcircuit for the rheostat motor 26 is completed extending from positivepotential through conductors 54 and 56, the contact element 50,conductors 58 and 60, the armature of the rheostat motor 26, conductors62 and 64, the contact element 52, and conductors 66 and 68 to negativepotential. When the relay 46 is released and the relay 40 is actuated,an energizing circuit of reversed pciarity is completed for the rheostatmotor ru extending from positive potential through conductors 54 and 56,the contact element 52 in the upper circuit closing position, theconductor bz, the armature of the rheostat motor 26, tne conductor 60,the contact element w, and the conductors 66 and 68 to negativepotential.

The energizing circuit for the rheostat motor 25 which is completed bythe actuation of the relay 46 will cause the rheostat motor to drive therheostat 24 in such a direction as to decrease the energization of theeld winding 69 of the main generator 2,to thereby decrease theenergization r and decelerate the motors 8, l0, 12, and l4'. When therelay 48 is actuated, the energizing circuit for the rheostat motor 26controlled thereby will cause the rheostat motor to actuate the rheostat24 in such a direction as to increase the energization of the heldwinding 69 of the main generator 2 to thereby accelerate the motors 8,l0, l2, and l4.

The relays 30, 32, and 34 are potential responsive relays connected torespond to the potential drops across shunt members '10, '12, and 14which areconnected in the energizing circuits of the motors 0, l0, andlz, respectively. Time-delayed pickup relays "u, 13, and 15 are disposedto be connected in an energizing circuit by the actuation of the relays30, 32, and 34. When the contact element lb of the relay ll is inthelower circuit closing position and the contact elements '18, 80, and 82of the circuit contro1 device 44' are in the left-hand position oppositeto the position shown in the drawing, the pilot generator 36 will beconnected to energize the relay 46. in a circuit extending irom oneterminal of the generator 36 through conductor 84, a resistor 85, aconductor 86, the contact element 16 of the relay "H, conductors 81 and88, the contact element 18, a conductor 90, a Variable resistor 92, aconductor 94, the winding of the relay 46, conductors 96 and 98, and aconductor 100 to the other terminal of the generator 36. The Variableresistor 92 may be adjusted so that its effective resistance value willbe such as to cause the relay 46 to pick up when the speed of the millmotor 8 is above the desired threading speed, and to be released when 4the rheostat 24 has caused the motor 8 to be decelerated to the desiredthreading speed.

When the end of a strip of material ll which is being threaded throughthe mill enters the roll stand IG, there will be a very considerableincrease in the load current of the motor 8, and this will cause therelay 30 to pick up to, in turn, cnergize the relay H. After the timedelay for which the relay H is calibrated or adjusted, the contactelement 16 of the relay 'Il will be moved from the lower circuit closingposition to the upper circuit closing position to disconnect the relay46 from the pilot generator 36 and to connect the relay 46 to beenergized by the pilot generator 38 ln a circuit which extends from oneterminal of the pilot generator 38 through a conductor l02, a resistorl03, a conductor l04, a contact element l of the relay 13 in the lowercircuit closing position, conductors l06 and'l08, the contact element16, the conductor 88, the contact element '18, the conductor 90, theVariable resistor 92, the conductor 94, the winding of the relay 46, andconductors 96, 98, and ll0 to the other terminal of the pilot generator38.

When the relay 46 is energized by the pilot generator 36, it will causethe rheostat 24 to further decrease the excitation and, therefore, theoutput potential of the main generator 2 to decelerate the motors 8, l0,I2, and I4 until the speed of the motor l0 has decreased to the desiredthreading speed. at which time the output potential of the pilotgenerator 38 will nave been decreased to where it is insuiilcient tofurther maintain the relay 46 actuated. When the end of the strip l0lenters the roll stand I8, the additional load on the motor l0 will causethe relay 32 to pick up and, in turn, energize the relay 13. After theinterval of time for which the relay 13 is calibrated or adjusted, itscontact element l05 will be picked up to disconnect the relay 46 fromthe pilot generator 38 and connect it to be energized by the pilotgenerator 40 in a circuit Which extends from one terminal of thegenerator 40 through a conductor M2, a resistor ll3, a conductor Il4, acontact element M5 of the, relay 15, conductors M6 and 8, thecontact-element l05, the conductor ios, the contact element 16, theconductor 68, the contact element 18, the conductor 90, the Variableresistor 92, the conductor 94,'the winding of the relay 46, andconductors 96, 98, and l20 to the other terminal of the generator 40.The actuation of the relay 46 will again cause the motors 8, l0, l2, andl4 to be decelerated until the speed of the motor l2 is such as toprovide the desired threading speed of the roll stand 20, at which timethe decreased potential of the pilot generator 40 will permit the relay46 to be released.

When the end of the strip l0l enters the roll stand 20, the relay 34will pick up to energize the time delay relay 15. After the timeinterval for which the relay 75, is calibrated, its contact element l I5will be moved to the upper circuit closing position to connect the pilotgenerator 42 to energize the relay 46 in a circuit which extends fromone terminal' of the generator' 42, a conductor i22, a resistor l23, aconductor I24, the contact element IIS, the conductor M8, the contactelement l05, the conductor l08, the contact element 16, the conductor86, the contact element 18, the conductor 00, the Variable resistor 92,the conductor 94, the winding'of the relay 46 az i conductors 96 and 98to the other terminal of the generator 42. The relay 46 will thus pickup to cause the deceleration of the motors 8, l0, l2,

and M until the motor 14 is running at such a speed as to provide thedesired threading speed r of the reducing rolls of the roll stand 22, atwhich time the pilot generator 42 will no longer maintain the relay 46actuated, and the relay 46 will be permitted to drop.

After the strip loi has been threaded through the mill, the motors 8,l0, l2, and l4 may be accelerated to the normal running "speed of themill by moving "the contact elements 18, 80, and 82 of the circuitcontrol device 44 to the right-hand position shown in the drawing. Whenin the circuit closing position, the contact element 82 will close anenergizing circuit for the lower winding of the relay 48 extending frompositive potential through a conductor l25, the contact element 82, aconductor l26, a lower winding of the relay 40, a conductor l28, acalibrating resistor l30, and a conductor i32 to negative potential. Therelay 48 will thus be actuated to cause the rheostat motor 26 to actuatethe rheostat 24 in such a direction as to increase the output potentialof the main generator 2 and thereby accelerate the motors 8, I0, 12, andI4. The upper winding of the relay 48 is connected to oppose the lowerwinding and is energized by the pilot generator 36 when the contactelement 80 is moved to circuit closing position in a circuit whichextends from one terminal of the generator 36, through conductors 84 and86', the contact element 80, a conductor l34, a calibrating resistor[36, a conductor l38, the upper winding of the relay 48, and conductors96, 98, and (00 to the other terminal of the generator 36. When the millhasbeen accelerated to the desired normal running speed, the outputpotential of the pilot generator 36 will have increased to such a degreethat its energization of the upper winding of the relay 48 will besumcient to counteract the energization of the lower winding of therelay 48 and cause this relay to be released, thus deenergizing therheostat motor 26 and discontinuing the acceleration of the mill.

It is to be understood that the upper winding of the relay 40 may beconnected by the circuit control device 44 to be energized by any of thepilot generators 38, 40 and 42 instead of the generator 36 as describedhereinbefore, to thereby control the speed of the mill in accordancewith the speed of any desired one of the roll stands.

It is to be understood that limit switches or other equivalent devicesWhich will respond to the position of the end of the strip which isbeing threaded through the mill, may be used iu the place of the loadrelays 30, 32, and 34 andtheir associated time-delayed relays H, 13 and15 to connect succeeding ones of the pilot generators 38, 40 and 42 tocontrol the decelerating relay 46.

It is also to be understood that the Variable resistor 92 may beadjusted so as to make the relay 46 responsive to any desired threadingspeed at the several roll stands. It is also to be understood that thecalibrating resistors [30 and l36 may be so adjusted as to cause themill to be acceierated to any desired normal running speed. Thetime-delayed-release relays H, 13 and 15 'may be adjusted to pick up ata suii'icient interval of time after the entry of the end of the stripi0l into the roll stands with which each of these relays are, associatedto permit the system to decelerate the mill until the next roll standinto which the end of the strip is to be threaded-has been deceleratedto the desired threading speed. The Variable resistors 85, l03, 3, andl23 are provided as calibrating resistors so that dierent prcvided ateach of the erated until the rolls of the roll stand l8 are running atthe desired threading speed. At a predetermined interval after the striphas entered the roll stand IB, the mill will be decelerated until therolls of the roll stand are running at the desired threading speed. At apredetermined interval after the strip has entered the roll stand 20,the mill will be decelerated until, the rolls of the roll stand 22 arerotating at the desired threading speed. With the mill thus threaded. itmay be accelerated to the normai running speed by moving the circuitcontrol device to the right-hand position shown in the drawing, and thesystem will automatically accelerate the mill to normai running speed,as explained hereinbefore.

Thus, a considerable saving inthe time required to thread a striprolling mill is made by the system sincenone of the reducing rolls aredecelerated below their desired threading speed until the end of thestrip which is being threaded through the mill has passed through thepreceding roll stand and it is necessary to decelerate the next rollstand to the desired threading speed.

Thus, it will be seen that I have provided a control system for a tandemstrip rolling mill which shall function to automatically provide thedesired threading speed for each succeeding roll stand as the end of astrip which is being threaded through the mill approaches each of thestands and which will thus function to permit threading of the mill in aminimumlength of time.

In compliance with the requirements of the patent statutes, I have shownand described herein a preferred embodiment of my invention. It is to beunderstood, however, that the invention is not limited to the preciseconstruction shown and. described but is capable of modification by oneskilled in the art, the-embodiment herein shown being merelyillustrative of the principles of my invention.

I claim as my'invention:

l. In a control system fora motor driven strip rolling mill, a maingenerator to which the mill motors are connected for energization, andmeans responsive to the speeds of the successive motors and thepositionof the end of the strip with respect to successive roll stands forautomatically controlling the potential of the'generator to provide thedesired threading speed at each succeeding roll stand as the end of astrip which is being threaded through the mill approaches eachsucceeding roll stand.

2. In a control system for the drive motors of a delayed relay meansresponsive to the entry of the end of a strip which is being threadedthrough the mill into one roll stand, means responsive to the speed ofthe drive motor for the next succeeding roll stand, and means responsiveto said relay means and said speed responsive means for varying thespeeds of the drive motors.

4. In a control system for the drive motors of a motor driven tandemstrip rolling mill, time delayed relay means responsive to the entry ofthe end of a strip which is being threaded through the mill into oneroll stand, means responsive to the speed of the drive motor for thenext succeeding roll stand, and means responsive to said relay means andsaid speed responsive means for reducing'the speeds of the drive motorssufficiently by the time the end of the strip reaches the saidsucceeding roll stand to provide the desired threading speed for the vsaid succeeding roll stand.

motor driven tandem strip rolling mill, means for varying the speed ofthe drive motors, and means 1 responsive to the speed of the drive motorassociated with one roll stand and the entry of the end of a strip whichis being threaded through the mill into the preceding roll stand forvarying the speeds of the drive motors associated with the roll stands.

3. In a control system for the drive motors of a motor driven tandemstrip rolling mill, time 5. In a control system for the drive motors oia motor driven tandem strip rolling mill, relay means associated witheach roll stand beyond which there is a succeeding .roll stand in thedirection of travel of a strip which is being threaded through the milland responsive to the entry of the strip into the associated roll stand,speed responsive means associated with each of the roll standssucceeding the fini; rc-ll stand, and means responsive to each relaymeans and the speed responsive device associated with the succeedingroll stand for reducing the speeds of the drive motors sumciently toprovide the desired ihre-riding speed for the said succeeding rollstand.

6. In a control system for the drive motors cf a motor driven tandemstrip rolling mill, time delayed relay means associated with each rollstand beyond which there is a succeeding roll stand in the direction oftravel of a strip which is being threaded through the mill andresponsive to the entry of the strip into its associated roll stand.means responsive to the roll speed of each of the roll stands succeedingthe first roll stand, and means responsive to said time delayed relaymeans and the speed responsive device associated with the succeedingroll stand for reducing the speeds of the drive motors sufficiently bythe time the end of the strip reaches the said succeeding roll stand toprovide the desired threading speed for the said succeeding roll stand.

7. In a control system for the drive motors of a tandem strip rollingmill, means for controlling the speeds of the drive motorssimultaneously, means responsive to speed of the rolls of each of theroll stands, means whereby each speed responsive means controls thespeed controlling means when connected for such control, means forconnecting the speed responsive means associated with the first rollstand to control the speed control means, and means responsive to theentry of the end of a strip which is being threaded through the millinto actuating said decelerating means until the speed of the first rollstand has been reduced to the desired threading speed for that rollstand, means responsive to the entry of the strip into any roll standwhich has a succeeding roll stand and the speed of the succeeding rollstand for actuating the mill decelerating means until the speed of thesaid succeeding roll stand has been reduced to the desired threadingspeed for that roll stand, and control means responsive to the speed ofone of the roll stands for causing said accelerating means to acceleratethe mill to normal running speed.

9. A control system for a tandem rolling mill having a plurality ofmotor-driven roll stands disposed to operate upon a strip of material,means for collectively varying the speeds of the motor-driven rollstands over a predetermined speed range between threading and normalrunning speeds, and electro-responsive control means operativelyassociated 'with the motordriven roll stands for controlling theoperation of the speed varying means, said electro-responsive meansbeing operable to effect successive reductions in the speeds of the rollstands in response to the entry of the end of the strip of material intoa preceding roll stand and the speed of the next succeeding roll stand,thereby to provide for progressively reducing the speeds of the rollstands during a threading operation.

10. A control system for a tandem rolling mill having a plurality ofmotor-driven roll stands disposed to operate upon a strip of material, amain generator to which the driving motors are connected, means forvarying the voltage of the main generator to simultaneously Vary thespeeds of the motors, and control means jointly responsive to apredetermined increase in the load of one motor and the speed of thenext succeeding motor for controlling the operation of the voltagevarying means, thereby to eiect successive reductions in the speeds ofthe roll stands as the leading end of the strip of material approacheseach succeeding roll stand.

11. In a control system for the driving motors of a tandem rolling millhaving a plurality of roll stands disposed to operate on a strip ofmaterial, a source of- Variable-voltage power for the motors, meansoperable to Vary the voltage of the power source to simultaneously varythe speeds of the motors between threading to normal running speeds,control means associated with each roll stand operable when connected tothe voltage control means to reduce the speed of its associated rollstand to a desired threading speed and to eifect a correspondingreduction in the speeds of the other roll stands, manually operablemeans for connecting the voltage control means to the control means ofthe rst roll stand, and additional control means associated with eachroll stand except the last roll stand operable in response tc tne entryof the leading end of the strip into the associated roll stand totransfer the connection of the voltage control means 'to the nextsucceeding control means, thereby to provide for reducing the speeds ofthe roll stands to the desired threading speed at each succeeding rollstand.

12. In a control system for the driving motors of a tandem rolling millhaving a plurality of roll stands disposed tc operate on a strip ofmaterial, a source of Variable voltage power for the motors, means forcontrolling the voltage of the power source to simultaneously Vary thespeeds of the motors, a pilot generator driven in accordance with thespeed of each roll stand and operable when connectzd to the voltagecontrol means tc cause said means to reduce the speed of all the rolldriving motors a predetermined amount from their normal running speeds,switch means operable to connect the pilot generator of the first rollstand to the voltage control means to effect a predetermined reductionin the speed of the nrst roll stand 'to a desired threading speed andcorresponding reductions of the speeds of the succeeding roll stands,and means associated with each roll stand except the last roll standoperable in response to theentry of the strip of material therein toconnect the voltage control means to be responsive to the pilotgenerator of the next succeeding roll stand, thereby to effectsuccessive reductions in the speeds of the roll stands as the end of thestrip approaches each succeeding roll stand during a threadingoperation.

13. In a control system for the driving motors of a tandem rolling millhaving a plurality of roll stands disposed to operate on a strip ofmaterial, a source of variablevoltage power for the motors, means forcontrolling the voltage of the power source to simultaneously Vary thespeeds of the motors, a pilot generator driven in accordance with thespeed of each roll stand and operable when connected to the voltagecontrol means to cause said means to reduce the speed of all the rolldriving motors a predetermined amount from their normai running speeds,switch means operable to connect the pilot generator of the first rollstand to the voltage control means to'.

eifect a predetermined reduction in the speed of the ilrst roll stand toa desired threading speed and corresponding reductions of the speeds ofthe succeeding roll stands, and load-responsive relay means associatedwith each drive motor except the last drive motor operable in responseto the entry of the end of the strip into its associated roll stand totransfer the connection of the voltage control means to the pilotgenerator of the next succeeding roll stand, thereby to eiect successivereductions in the speeds of the motors as a group as the end of thestrip approaches each succeeding roll stand during a threadingoperation. v

14. In a control system for a tandem rolling mill or the like, having aplurality of roll stands disposed to operate upon a. strip of materialand a motor connected to drive each roll stand, a main generatorforsupplying Variable voltage power to the motors, a motor-operatedrheostat operable to Vary the voltage of the main generator, relay meansselectively operable to control the operation of the motor-operatedrheostat, a pilot generator connected tc each roll stand operable todevelop a voltage in accordance with the speed of the associated rollstand, a load responsive relay connected to each drive motor except thedrive motor of the last roll stand, a timedelay relay controlled by eachload-responsive relay, said load-responsive relays, timerdelay relaysand pilot generators being electrically interconnected and connected tothe relay means for controlling the operation of the motor-operatedrheostat to eect a progressive reduction in the speeds of the rollstands as the leading end of the strip of material passes through themill, whereby the desired threading speed at each roll stand is obtainedbefore theleading end of the strip enters the rolls.

GLENN E. STOLTZ.

